This invention relates generally to the reconstruction of images and more particularly to methods and apparatus for 3D (three dimensional) reconstruction of images using virtual parallel sampling and/or view weighted backprojection.
With the development of three-dimensional (3D) or cone beam (CB) filtered backprojection (FBP) reconstruction algorithms, multi-detector-row CT scanners are evolving into volumetric CT (VCT) scanners. One of the most practical CB FBP reconstruction algorithm is the “FDK” algorithm proposed by Feldkamp, David and Kress in “Practical cone beam algorithm,” J. Opt. Soc. Am. A, vol. 1, pp. 612-619, 1984. A helical FDK algorithm to handle helical CB data acquisition geometry is described in G. Wang, T. H. Lin, P. C. Cheng and D. M. Shinozaki, “A general cone-beam reconstruction algorithm,” IEEE Trans. Med. Imag., vol. 12, pp. 486-496, 1993.
One common feature of both the original FDK and helical FDK algorithms is a 1/L2 factor in the 3D backprojection, in which L is the distance between the x-ray focal spot and the image pixel to be reconstructed. It is well recognized that the location-dependent 1/L2 factor results in computational complexity in the backprojection and non-uniform noise characteristics in tomographic images. To overcome these shortcomings, a modified FDK algorithm is described in U.S. Pat. No. 6,263,040 B1 (assigned to General Electric Company) by removing the 1/L2 from the 3D backprojection, in which a sequential triggering technique is employed to obtain cone-tilted parallel sampling (namely real 3D parallel sampling) from 3D cone sampling. However, this sequential triggering technique involves increased design and manufacturing complexities.